Selectively illuminated traffic control signals and/or similar devices are so commonly used as to be familiar to anyone walking along public streets or riding in a vehicle along public highways. Among other things, traffic lights are used to regulate the flow of both automotive and railroad traffic or a combination thereof. For example, where a highway crosses a railroad track, it is common to see a traffic light visible to the highway traveler and which serves to warn that a train is approaching the intersection.
As is well known, traffic lights typically employ an incandescent lamp together with a reflector system which collects and focuses the light so that the emitted light rays are concentrated in a beam which may be most readily seen by the pedestrian and/or driver for whose benefit the signal light is placed. In order to be energy efficient, it is customary to use curved reflectors in association with the lamp to collect and focus the light rays so that they are emitted essentially parallel to the axis of the reflector, or at a small angle of dispersion with respect thereto. Occasionally, circumstances are such that at selected times of the day, or year, light from an external source, most commonly the sun, can enter the signal through the front, be reflected one or more times by the reflecting surface and re-emerge in such a way as to simulate a normal signal from the lamp. Such apparent signals resulting from light originating externally are customarily referred to as "phantom" signals and can give rise to unsafe, confusing and ambiguous conditions. For example, a typical traffic light which may have the three colors red, yellow and green, indicating stop, caution and go, respectively, may receive sunlight and creats a simultaneous phantom signal from each of the three reflectors thereby providing a confusing or ambiguous signal to the highway traveler. Because phantom signals can cause confusion and accident, considerable inventive ingenuity has been exercised in an attempt to eliminate or minimize phantom signals. For example, U.S. Pat. No. 2,097,785 issued Nov. 2, 1937 to O. S. Field and assigned to the same assignee as the present invention teaches the use of funnel-shaped members having longitudinal corrugations to reflect light to non-parallel paths to thereby minimize or eliminate phantom signals. U.S. Pat. No. 2,207,656 issued July 9, 1940 to C. H. Cartwright, et al, teaches the treatment of the surface on the front lens whereby to render the lens non-reflective. U.S. Pat. No. 2,243,448 issued May 27, 1941 to W. B. Wells, et al, teaches phantom elimination in a specialized light signal having at least two optical systems and provides means for preventing light rays entering a signal from a foreign external source through one optical system from causing the other optical system to display a phantom signal. U.S. Pat. No. 2,286,201 to C. L. Ferrin, et al, employs an internal apertured plate and a front element comprising a plurality of lenses. U.S. Pat. No. 2,336,680 issued Dec. 14, 1943 to S. E. Gillespie provides phantom elimination by light-polarizing means. U.S. Pat. No. 2,413,127 issued Dec. 24, 1946 to W. B. Wells uses a conical roundel to prevent reflection of light from an external source. Other patents disclosing structures relating to phantom signals include U.S. Pat. Nos. 2,419,444; 2,576,849; 2,750,577; 3,235,863; and 3,377,479.